The invention relates to the field of tray forming and more particularly to a method and apparatus for forming a stackable tray having reinforcement and sealing flanges around the top of the tray.
In the packaging art it has been common practice to form cartons and trays from coated paperboard or the like. An exemplary carton folding machine is shown in the patent to Baker et al., U.S. Pat. No. 2,655,843, issued Oct. 20, 1953 in which a vertically reciprocating plunger forces a paperboard blank into a die-forming cavity to erect the side walls of the carton and simultaneously join the corners.
Recently, with the increased popularity of packaged convenience foods, there has been a trend in the industry to provide a coated paperboard tray which can be placed directly in an oven (conventional or micro-wave) to heat the contents thereof and which can also be used as a serving tray for the food items after heating. This is becoming a very popular item for home use. Such an arrangement is also particularly advantageous when used in establishments where a large volume of food must be cooked and used within a short period of time such as the airline industry or in hospitals, since the food can be prepared ahead of time and frozen and then quickly reheated for serving. In addition, since the serving trays are disposable preparation and washing of dishes is eliminated.
The trays must be strong to prevent collapse during handling. Also, in order to keep the food warm after cooking, it is desirable to have some type of lid for the tray. Indeed, many foods must be cooked while sealed, in order to retain moisture and the flavor of the food.
One approach to provide a strong sealed tray is to form a flange of paperboard along the edges of the tray walls and provide a surface to which a cover can be sealed. The forming of a flanged, sealable tray, is a complex operation, since not only must the side walls of the tray be simultaneously erected and the corners glued, but the flanges must be overbroken; i.e., the flanges folded sufficiently to cause them to lie at approximately right angles to the tray wall when released.
The ends of the flanges preferably overlap slightly and may be adhesively bonded to create the secure, rigid "collar" around the upper edges of the tray walls. A lid is then sealed to the upper surfaces of the flanges.
The prior art machinery for forming such flanged, sealable trays is complex and operates quite slowly since not only must all the walls of the tray be quickly erected, but the tray must be secured in its erected position while the corner and flange adhesive sets. The paperboard blank is first forced into a die or cavity by means of a reciprocating plunger to erect the tray walls. The traydrops on to a conveyor or shelf and separate clamping means holds the tray in this position while the flanges are turned down. When the tray is in this position, it is held until the adhesive has sufficient time to set. Thus, there are serious limitations on throughput in present carton forming machines due to the necessity for separately forming the flanges and for retention of the carton in its erected position while the adhesive sets before the next carton blank can be handled.
It is thus an object of the invention to provide an improved method and apparatus for rapidly forming a stackable, flanged tray from a paperboard blank.
It is another object to provide the method and apparatus for forming a flanged tray which can be stacked immediately after forming.
It is yet a further object to provide a method and apparatus for forming a stackable, flanged tray in which the flanges are folded in an overbroken position with respect to the carton walls simultaneously with the forming of the tray itself.
It is an additional object to provide a method and apparatus for forming a flanged tray which is unusually strong and readily sealed after forming.